ABSTRACT
This paper first analyzes the voltage compensation issue of super capacitor-based unified power quality controller (SC-UPQC). On one hand, taking rated voltage of load as the reference, the constraint condition of the compensation strategy of SC-UPQC is demonstrated. On the other hand, the concept of the change rate of the amplitude of series voltage compensation is introduced. Taking the rated voltage of load as the reference, the range of compensation voltage and current in the series and parallel units of UPQC is further analyzed. Then, as the SC-UPQC is able to solve the problem of insufficient energy storage of active power, a new compensation strategy based on a parallel unit with constant apparent power after fault occurrence is proposed. By choosing appropriate parallel compensation current, the proposed compensation strategy can achieve the reasonable distribution of active and reactive power between power grid and series-parallel unit. Therefore, the compensation capacity of the series-parallel unit is optimized, and can compensate the voltage in the faults like voltage swells and sags. A simulation model is established in Matlab/Simulink. The simulation results verify the effectiveness of the proposed compensation strategy.
